End of day though the question was can silicic acid act like a PGR (growth retardant) and that is a no
You should ask someone else, because it does stunt with high dosage. Plants aren't used to high Si because high Si is unnatural. Natural Si comes to plants from infinitesimally slight surface depolymerization of polymerized Si material in water. This is why the very finely ground DE is a good source of Si, because of the large surface area. Plants absorb the Si and fill their leaves and stems with it and then it will mess with things because there's no way for the plant to get rid of it, once it's polymerized inside.
Fasilitor is not a simple solution of potassium silicate, which is a strong base that can affect nutes by pH and metal silicate precipitation, and forms polymers almost instantly when acidified. Fasilitor does not affect pH much or at all. If it stunts plants easily, that's kind of proof that it really is PAS.
Analysis of Fasilitor wouldn't be as helpful as analyzing the plants for actual Si uptake from it. This is the real missing information from Aptus.